Various types of bulk materials are often stored in large structures (or sometimes just in large piles) until it is necessary to use them. This may include, for example, bulk materials which are fibrous, granular, or finely divided materials. Common examples of such materials are silage, wood chips, coal, grain, and the like. Where storage structures are used they are commonly cylindrical and may be of various diameters and heights. Other types of storage structures may have a length greater than their height and may have a floor or base section sloped toward a low point (which may be the center of the structure, for example).
When it is desired to remove some amount of the material from such storage means, it is normally not possible to simply open a door at the bottom of the storage means in order to let the material flow out. Fibrous materials, for example, will not flow. Finely divided or granular materials often will not flow properly if they become wet, frozen, or packed so tightly that they are bound together.
Although the bulk material could instead be removed from the storage means from the top side, this would require that an upright structure have a series of doors or other such access openings at various heights in the wall of the structure. This not only adds to the expense of the structure but it also increases the likelihood that undesirable air leakage into the structure will result. This would also require that the unloading apparatus be adapted to deliver bulk material out one of the openings in the wall irrespective of the level of bulk material in the structure.
The use of bottom unloading devices is very desirable because the storage structure may be kept sealed, if necessary. Furthermore, there is no need to utilize a series of vertically spaced doors in the wall of the storage structure.
Various types of bottom unloading devices have been proposed for use in unloading silos and grain bins. These unloading devices typically include a sweep arm which pivots around a central opening in the floor of the structure. The arm conveys bulk material to the central opening where other conveyance means transports the material beyond the outer wall of the storage structure.
Some of these prior devices utilize a circular track on the floor of the storage structure to guide and, in some designs, to actually drive the outer end of the sweep arm around the floor. In some of these designs the track is located at a point between the center and the wall of the structure. See, for example, U.S. Pat. Nos. 1,275,558; 2,914,198; 3,289,862; and 3,367,519. In other designs the circular track is disposed within a recess in the wall. See, for example, U.S. Pat. Nos. 3,282,446; 3,298,543; 3,121,501; and U.S. Pat. No. Re. 25,863. In still another design the circular track is adjacent the wall of the structure. See U.S. Pat. No. 3,237,788.
There are many disadvantages associated with these former designs. For example, special installation of the equipment is required. The circular track can only be installed when the storage structure is empty. Where the design requires a track recessed in the wall of the structure, it is necessary for the structure to be specially designed in order to accommodate the apparatus. As a practical matter, apparatus of such design would be used only in storage structures which had been built so as to specially accommodate such apparatus.
Where the design relies upon a separate motor inside the storage structure to drive the outer end of the sweep arm, additional complications are presented. Not only is there the greater risk of equipment failure owing to the presence of a second motor, there is also additional drive equipment within the storage structure which must be operating properly in order to produce the desired result.
Various other types of bottom unloading devices have been described in the literature and many have been commercialized. For example, see the following U.S. Pat. Nos.: 2,969,156; 2,711,814; 2,934,224; 2,675,931; 2,635,770; and 3,298,543.
All of the foregoing types of apparatus for unloading a storage structure involve an auger or chain mechanism which rotates at the same rate of speed along its full length, i.e., each portion of the auger or chain mechanism moves at the same rate, because the auger and chain are unitary items. This requires that an exceedingly high amount of energy be supplied to the mechanism initially in order to start the entire mechanism in motion. When the conveyor is covered by the bulk material, the start-up load on the conveyor is extremely high and may exceed the normal operating load by several fold. Thus, it has been necessary to design the conveyor in a manner such that the entire apparatus (i.e., power source, drive train, and working portions) is capable of withstanding the very large forces associated with starting under load. This, of course, has a significant effect on the cost and size of the components used in the construction of the apparatus.
The present invention provides apparatus which overcomes these limitations and disadvantages.